This invention relates to a process for manufacturing vermicular graphite cast-iron by a double modification. Processes for manufacturing vermicular graphite cast-irons are already known. One process modifies the liquid cast-iron in a single phase with modifying alloys which contain both compactizing (Mg, Ce) and anticompactizing (Ti, Al) elements for the graphite. A second known process modifies the iron in a single step with rare-earth elements. A third process is to treat liquid cast iron with metallic zirconium or with an alloy containing zirconium and magnesium.
These processes have the disadvantage that the alloy or modifying element ratio must be adjusted depending on the initial sulphur content of the liquid cast-iron, the modifying temperature and the holding time in the liquid state after modifying, and that inconsistent vermicular graphite ratios in the cast-iron structure result and thus the mechanical characteristics of the poured cast iron are not constant.